“The Sessions” is an ungainly and uncinematic but ultimately affecting treatment of an interesting true story, made all the better by its refusal to talk down to audiences and its insistence on treating adults like adults. Even if it’s visually flat, that in itself makes “The Sessions” fairly unique and refreshing, and coupled with a pair of terrific performances, one Oscar-nominated and one surprisingly not, it’s the sort of thing that discerning audiences have found the cinema lacking in recent years.

First and foremost, “The Sessions” is about sex and religion, their importance in the life of an adult and the intersection between matters of the divine and matters of the flesh. In a culture in which sex is reduced most often to a punchline in film (see, for example, every other movie in theaters right now), “The Sessions” is clearheaded and sweet-natured, even if, when you want to boil it down, it’s also about a man seeking to lose his virginity.

What makes it not the same old story is that the man in question, Mark O’Brien (John Hawkes), is 38 years old and has spent most of his life confined to an iron lung, a result of being crippled at a young age by polio. A poet and journalist who works from home most of the time, requiring constant attention from caretakers, O’Brien decides, after falling in love with a young woman (Annika Marks) in his employ, to seek assistance in losing his virginity. Fiercely Catholic, he consults with his priest (William H. Macy), who gives him the go-ahead. And a tip from a story he’s working on leads him to a sex surrogate, Cheryl Cohen-Greene (Academy Award nominee Helen Hunt), a therapist who works with the sexually frustrated and damaged, who is allowed six sessions with the repressed O’Brien to teach him about his body, with his caretaker (Moon Bloodgood) and priest as his only confidants on the journey.

As you can tell, “The Sessions” is fairly prurient and frank, but never in an exploitative fashion. It’s graphic and candid (in that Hunt is frequently totally naked), but maturely depicted, with respect and sweetness. O’Brien seeks a connection and friendship as much as anything else, but as a professional therapist obligated to not cross a line, Cohen-Greene can only provide him with so much.

Yet the film doesn’t seem interested in engaging in any real conflict apart from O’Brien’s religious guilt; even the life-or-death stakes of his condition seem muted, engaged with if only to pay lip service to his unusual circumstances. Subplots involving Cohen-Greene’s home life (featuring Adam Arkin as her husband, who’s incredibly understanding about her job, until he isn’t) seem miscalculated. And Bloodgood seems saddled with a blank, thankless role, despite an increasing prominence in the story.

That the film is acted with such sensitivity is a testament to its actors, especially considering Hawkes is limited in his expressions — apart from the contortions of his body needed to portray a paralyzed victim of polio — to above his neck. And Hunt is quite effective, earthy and sensitive, and I believe the word traditionally used for middle-aged actresses who are this nude throughout a film is “brave.”

Writer-director Ben Lewin is to be commended for drawing together this cast and for writing the screenplay that provides them with strong material, but the film’s look is generally undistinguished and flatly lit. This is Lewin’s first feature, and one close to his heart, given the director also was afflicted with polio as a child. It’s just successful enough — with its fine performances and moments of true beauty, often courtesy of the real O’Brien’s writing — to be worthwhile for adult audiences.